Recently, use of multimedia communication such as image communication, voice communication, high-speed data communication is increasing with widespread use and expansion of the internet, and communication service suited for data communication of large capacity is being desired. The line side must be able to transmit large capacity of data as in optical fiber network, and furthermore, the exchange node such as router must be able to process the large capacity of data in order to perform data communication of large capacity, and higher performance of the exchange node is being advanced.
The configuration of the exchange node used in the conventional connectionless type IP (Internet Protocol) data communication is shown in FIG. 22. In FIG. 22, the reference numeral 81 is denoted for an input side line control unit for writing input data 87 from an external transmission path, 82 for a common control unit for performing routing control, 83 for a common memory, 84 for a common bus, 85 for an output side line control unit for controlling the input data 87 towards the direction path of the outgoing line, and 86 for a multiplexing unit. Furthermore, 90 is denoted for a conventional exchange node, 88 for an input side clock, and 89 for an output side clock in FIG. 22. A dotted line from the input data 87 to the output side line control unit 85 indicates the flow of packet transfer. The dotted line connecting the input side line control unit 81 and the common control unit 82 and the dotted line connecting the input side control unit 81 and the common memory 83 indicate update and the like of a routing table.
The flow of input data in FIG. 22 will now be described. The input data 87 is input to the input side line control unit 81, and written in a shift register. After all the input data 87 are written in the input side line control unit 81, the input data 87 is output to the common bus 84. The input data 87 outputs to the common bus 84 is written in the common memory 83 to be performed with routing control in the common control unit 82. The common memory 83 holds the input data 87 until the turn of the input data 87 to be performed with the routing control, and again outputs the input data 87 to the common bus 84 when its turn for control arrives. The input data 87 performed with routing control in the common control unit 82 is input to the output side line control unit 85, and output to the direction path corresponding to the direction path information contained in the input data 87. The output data is multiplexed to one bus in the multiplexing unit 86, and transmitted to the outgoing line.
However, a great number of buffers such as the input side line control unit 81, the common memory 83, the output sideline control unit 85 are required in the exchange node used in the conventional connectionless type IP data communication, as described above, and such buffer processes produce the delay time in the communication. Moreover, when accommodating lines of different communication speeds in a mixed manner, an uncertain delay time that cannot be assured is produced depending on the traffic congestion state that occurs when lines of the same communication speed are used in the same period of time thereby inhibiting the enhancement of real-time property.
An ATM (Asynchronous Transfer Mode) technique has been proposed as a technique of improving the delay time in communication. In the ATM method, the signals of each channel are divided into packets referred to as cells of fixed length regardless of their speed, and sent in an asynchronous manner. A mechanism of writing a channel number in the header of the cell at the transmission side and sending the cell is adopted so that each channel can be identified on the reception side. A priority control that takes the delay time into consideration is possible in the exchange node adopting the ATM method, but it is essentially difficult to completely guarantee the quality of real-time communication when the amount of flow-in traffic differs greatly from the expected value such as fluctuation in delay time or loss of packet when unexpected traffic load flows in since the relevant method assumes that the buffer control is performed in the exchange node.
A communication model when transferring voice as IP data is shown in FIG. 23. RTP (Real Time Protocol) is a protocol for controlling the order of data by a time stamp, and reproducing the data in the transmitted order, but UDP (User Datagram Protocol) is used in the transport layer in voice communication. Generally, the connectionless type UDP is used on the Internet since greater throughput of information transfer can be performed compared to the TCP. The UDP does not have the function of re-ordering the order of arrived data to the original order, error restoring function of performing restoration or the like, and thus lacks in reliability and adequate voice quality may not be guaranteed. In the connection type communication, compliance with respect to the communication quality is possible within a reference range defined in advance in the network, but the connectionless communication must sometimes be used due to problems in that the overhead in communication necessary in call set up control is large and the call set up time until starting the communication is long since it takes a great amount of processing time when occupying the line corresponding to a specific logic channel for communication, the software control on the terminal side and the exchange node side involved in call set up control is complex etc. (e.g., see non-patent document 1).
A case of performing priority control transfer of IP data and the like on the premise of connection type communication by discarding the common control buffer used in the conventional exchange node and router, and utilizing instead, an ultra high-speed electronic circuit or superconductive element for communication path common bus has been described.
Such method shows a possibility of avoiding a phenomenon in which an uncertain delay time that cannot be assured is produced due to waiting time in the common buffer and the output line buffer. However, a technical countermeasure for constantly guaranteeing stable quality in the exchange node is required in the connectionless type communication, and real time communication in which interactive voice, picture information are targets and in which a variety of communication quality (QoS: Quality of Service) and high-quality communication precision or the like are required. In particular, realization of the method of resolving the problems related to the delay time of the exchange node is being desired in the connectionless type communication in which the overhead in communication required for the setting control of calls is not present.
A priority control method referred to as Diffsery (Differentiated Services) method has been conventionally developed as a connectionless type communication method of controlling the quality with respect to voice, specific application flow and the like. In the Diffserv method, the priority information is given to each IP packet to be transferred by the user so that a relative transfer performance difference is created between a plurality of priority classes, whereby the internet user is able to identify the type of traffic to be transmitted and received without using the signaling procedures, and provide the communication quality corresponding to the relevant type, but the problems related to the delay time in the exchange node are not resolved depending on the communication traffic congestion state even with the Diffserv method.
[Non-patent document 1] Noriharu Miyaho and two others, “Basis of latest computer network technology”, The Telecommunication Association, Nov. 1, 2003, p. 3-214